Guys who are running power discs with low vacuum - Team Camaro Tech
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post #1 of 11 (permalink) Old May 18th, 10, 08:46 PM Thread Starter
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Guys who are running power discs with low vacuum

I think I'm finally going to start installing the power disc brakes on the Camaro.
The only problem I can think of is, my motor makes about 5"-7" of vacuum at best. The stuff I got was from a guy who pulled it off his '69, a re manufactured power booster, 11" front discs, single piston calipers, a vette master cyl, and a few other odds and ends, including a vacuum canister.

I'm thinking with the low vacuum even with the canister, the brakes will be really hard, especially with the bigger vette master cyl.
Can some others chime in and give some advice on this issue?
Would it be better just to run them manual?
Would a smaller master cyl work?
and what RPM drop when the brakes are applied at idle can I expect? if my motor drops below about 700rpm it starts to die out due to the vacuum advance canister (working on that issue as well)

The only Mustang I'd ever own is a Fender.

'68 333" Camaro
'14 5.0 Mustang
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post #2 of 11 (permalink) Old May 18th, 10, 08:53 PM
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Re: Guys who are running power discs with low vacuum

I think your only option is a hydro booster master cylinder.... You don't want to have to run a vacuum pump.

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post #3 of 11 (permalink) Old May 18th, 10, 10:03 PM
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Re: Guys who are running power discs with low vacuum

Once you are under light load moving down the road, what kind of vacuum reading do you get? Or when you pat the throttle at idle what do you get? You should be able to get at least 15" of vacuum at light load which is enough to charge the booster for two or three brake applications. I don't think you'll have an RPM drop with the brakes applied unless there's a leak in the booster. The Z/28 was available with power brakes and I don't think it made very much idle vacuum.

Personally, I would put them on and try them before putting any more money into it. Unless you are driving in stop and go traffic where all you're doing is slipping the clutch to move and then stop you may find that the setup isn't exactly terrible. I drove mine initially with a bad check valve so it wasn't storing vacuum on the booster (anything above engine vacuum anyway) and it still stopped about a hundred times better than with manual drums.

'69 Camaro
Dart 400-AFR 195-224/224 HR-Powerjection III TB with F.A.S.T. Sportsman XFI
TKO 600-Moser 3.42-Detroit Truetrac
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post #4 of 11 (permalink) Old May 18th, 10, 10:32 PM
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Re: Guys who are running power discs with low vacuum

This question has been asked many times..
Run a forum search
The only time in real life practical terms is when say, isling slow out of a gas station, use the brake, then release them maybe use again its not powerassited
9 time out 100 ten event then it is rare u will lift off and put down cause you will have constant pressure.

My Spelling is not incorrect...it is creative

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post #5 of 11 (permalink) Old May 18th, 10, 10:34 PM
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Re: Guys who are running power discs with low vacuum

Also, the check valve holds the highest level of vacuum your engine has created.
So, when you are decelerating and making 20" of vacuum thats going straight into the booster.
You could also get a dual diaphragm booster, with more surface area they can give more assist.
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post #6 of 11 (permalink) Old May 19th, 10, 12:10 AM Thread Starter
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Re: Guys who are running power discs with low vacuum

Thanks for the info guys.
I will put a vacuum gauge on the motor and tape it to the cowl and drive around. I can say though, when rpm's are increased slightly at idle, the vacuum jumps up pretty high, and I do have to slip the clutch to at least 2k to get a good moving start, so that will help, I think I could learn to live with it, if the brakes are too hard, I'll probably change out the big master cyl.
I should have done the search first, but the search will usually pull every result that has any key word in it, which amounts to a lot of time sorting through all the irrelevant posts.
Again, thanks for the info. I'll be installing them in hopefully 2 weeks and post back!

The only Mustang I'd ever own is a Fender.

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'14 5.0 Mustang
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post #7 of 11 (permalink) Old May 19th, 10, 01:13 AM
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Re: Guys who are running power discs with low vacuum

Just get yourself a long length of vacuum tubing. They usually have the Thermoid stuff and T's together. Then you can run the gauge in through the window. Did that once when trying to troubleshoot something on my truck. I've got a vacuum gauge in the car though.

'69 Camaro
Dart 400-AFR 195-224/224 HR-Powerjection III TB with F.A.S.T. Sportsman XFI
TKO 600-Moser 3.42-Detroit Truetrac
500hp/538lbft

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post #8 of 11 (permalink) Old May 19th, 10, 01:38 AM Thread Starter
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Re: Guys who are running power discs with low vacuum

Thanks steiner, I've got a t fitting, and alot of vacuum hose laying around, I really need to install more gauges in the car like vacuum and a/f.
Also, where are people mounting the vacuum canisters under the hood?

The only Mustang I'd ever own is a Fender.

'68 333" Camaro
'14 5.0 Mustang
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post #9 of 11 (permalink) Old May 19th, 10, 02:07 AM
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Re: Guys who are running power discs with low vacuum

I bought a can but wound up not installing it since the four wheel power discs and 11" booster seem to work fine as is. If I were going to put one in I'd probably just mount it on the back side of the passenger inner fender or where the windshield washer reservoir is since mine's not hooked up anyway. I'll bet after you drive it a little you'll find that you might not need the can. It's something that could always be added later. The can isn't going to do anything but give you a couple more pumps of the brake if the booster hasn't recharged.

'69 Camaro
Dart 400-AFR 195-224/224 HR-Powerjection III TB with F.A.S.T. Sportsman XFI
TKO 600-Moser 3.42-Detroit Truetrac
500hp/538lbft

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post #10 of 11 (permalink) Old May 19th, 10, 09:42 AM
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Re: Guys who are running power discs with low vacuum

i like the feel of my manual disc system. although its a little over-kill w/13' front and 12'' rear

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post #11 of 11 (permalink) Old May 19th, 10, 02:49 PM
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Re: Guys who are running power discs with low vacuum

I used to run 5 to 6" of vac on one of my old cams
other than the issue I mentioned above...on rare occassions never had a problem

I have run a vac gauge in the car for near on 30 yrs
mounted by the scews under the dash below the wiper switch.
The vac hose is T ed off the VA (manifold vac) thru the firewall, cant rem which hole I used.....and the light inside connected into the dash light circuit...even changed the bulb to a green one.
Without a vac gauge inside the car one cant set VA specs and a lot of other stuff.

My Spelling is not incorrect...it is creative

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